substring index range

Code:

public class Test {
public static void main(String[] args) {
String str = "University";
System.out.println(str.substring(4, 7));
}
}

Output: ers

I do not really understand how the substring method works. Does the index start at 0? If I start with 0, e is at index 4 but char i is at 7 so the output would be ersi.

164832 次浏览
小开

See the javadoc. It's an inclusive index for the first argument and exclusive for the second.

小开

Both are 0-based, but the start is inclusive and the end is exclusive. This ensures the resulting string is of length start - end.

To make life easier for substring operation, imagine that characters are between indexes.

0 1 2 3 4 5 6 7 8 9 10  <- available indexes for substring
u n i v E R S i t y
↑     ↑
start  end --> range of "E R S"

Quoting the docs:

The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

小开

Yes, the index starts at zero (0). The two arguments are startIndex and endIndex, where per the documentation:

The substring begins at the specified beginIndex and extends to the character at index endIndex - 1.

See here for more information.

小开
最佳答案

0: U

1: n

2: i

3: v

4: e

5: r

6: s

7: i

8: t

9: y

Start index is inclusive

End index is exclusive

Javadoc link

小开

Like you I didn't find it came naturally. I normally still have to remind myself that

  • the length of the returned string is

    lastIndex - firstIndex

  • that you can use the length of the string as the lastIndex even though there is no character there and trying to reference it would throw an Exception

so 

"University".substring(6, 10)

returns the 4-character string "sity" even though there is no character at position 10.

小开

For substring(startIndex, endIndex), startIndex is inclusive and endIndex are exclusive. The startIndex and endIndex are very confusing. I would understand substring(startIndex, length) to remember that.

小开

The substring starts at, and includes the character at the location of the first number given and goes to, but does not include the character at the last number given.

小开 
public String substring(int beginIndex, int endIndex)

beginIndex—the begin index, inclusive.

endIndex—the end index, exclusive.

Example:

public class Test {


public static void main(String args[]) {
String Str = new String("Hello World");


System.out.println(Str.substring(3, 8));
}
}

Output: "lo Wo"

From 3 to 7 index.

Also there is another kind of substring() method:

public String substring(int beginIndex)

beginIndex—the begin index, inclusive. Returns a sub string starting from beginIndex to the end of the main String.

Example:

public class Test {


public static void main(String args[]) {
String Str = new String("Hello World");


System.out.println(Str.substring(3));
}
}

Output: "lo World"

From 3 to the last index.

小开 
public class SubstringExample
{
public static void main(String[] args)
{
String str="OOPs is a programming paradigm...";


System.out.println(" Length is: " + str.length());


System.out.println(" Substring is: " + str.substring(10, 30));
}
}

Output:

length is: 31


Substring is: programming paradigm

提交答案